The present application is based on Japanese Patent Application No. 2001-60972, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a light-emitting device provided with a light-emitting element. The light-emitting device according to the invention may be used, for example, as a light source for illumination or as a light source for any kind of display device.
2. Description of the Related Art
A configuration shown in FIG. 6 is known as the configuration of a light-emitting device using a light-emitting element. FIG. 6 typically shows an SMD (surface mounted device) type LED 100. In the LED 100, a cup-like portion 150 is formed on a substrate 120 and a case (reflector) 130, and a light-emitting element 110 is disposed in the cup-like portion 150. Further, the cup-like portion 150 is filled with a sealing member 140 (of a light-transmissible resin).
A surface of the case 130 facing the light-emitting element 110 are selected to have such a shape and a material so that light irradiated from the light-emitting element 110 onto the surface can be reflected by the surface so as to be used as light in a direction of an optical axis. For example, a shape shown in FIG. 6 is made of a white resin which contains a white filler dispersed in a polymer resin. The case 130 configured as described above is used so that light irradiated from the light-emitting element 110 onto the surface of the case 130 can be partially converted into light in the direction of the optical axis so as to be radiated to the outside.
In the LED configured as described above, a part of light which has been emitted from the light-emitting element 110 and has reached the surface of the case 130 is irregularly reflected or diffused by the surface of the case 130, so that the part of light cannot be used as light radiated to the outside. This unfavorable result is assumed to be caused by the light reflected by the surface of the case 130 which is a surface of the filler grains (different from a flat surface having a predetermined angle to irradiated light). As described above, it cannot be said that the light-emitting device having the related-art configuration can utilize light emission of the light-emitting element sufficiently and effectively. There is still a room for improvement in emission efficiency.
The invention is developed in consideration of these circumstances, and an object of the invention is to provide a light-emitting device which can emit light with high luminance by effectively using light emitted from a light-emitting element.
To achieve the foregoing object, the invention uses the following configuration.
A light-emitting device having:
a light-emitting element;
a case including a cup-like portion having a bottom on which the light-emitting element is mounted;
a sealing member with which the cup-like portion is filled so that the light-emitting element is covered with the seal material; and
a low-refractive-index layer having a refractive index lower than that of the sealing member and formed between the sealing member and a surface of the case shaping a side surface of the cup-like portion.
In this configuration, the sealing member and the low-refractive-index layer are disposed between the light-emitting element and the surface of the case shaping the cup-like portion, in the order of increasing distance from the light-emitting element side. Hence, light emitted from the light-emitting element and traveling toward the surface of the case (that is, light emitted in a direction of alienation from an optical axis) passes through the sealing member and is made incident on the low-refractive-index layer. On this occasion, among light incident from the sealing member side onto the low-refractive-index layer, rays having incidence angles of not lower than a predetermined angle are totally reflected by the interface between the sealing member and the low-refractive-index layer because the refractive index of the low-refractive-index layer is lower than that of the sealing member. That is, the interface serves as a reflection surface, so that light incident on the low-refractive-index layer can be reflected by the interface so as to be converted into light in the direction of the optical axis. As a result, externally radiant efficiency is enhanced so that light can be emitted with high luminance. According to the inventors"" examination, it has been found that a light-emitting device with very high luminance is formed by use of this configuration. Details of this finding will be understood by referring to the following description of embodiments.
As described above, a light-emitting device with high light-emitting efficiency can be provided because the configuration of the invention is quite different from the related-art configuration in that the interface between the sealing member and the low-refractive-index layer is used as a reflection surface.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.